GDF11: An emerging therapeutic target for liver diseases and fibrosis

Abstract Growth differentiation factor 11 (GDF11), also known as bone morphogenetic protein 11 (BMP11), has been identified as a key player in various biological processes, including embryonic development, aging, metabolic disorders and cancers. GDF11 has also emerged as a critical component in liver development, injury and fibrosis. However, the effects of GDF11 on liver physiology and pathology have been a subject of debate among researchers due to conflicting reported outcomes. While some studies suggest that GDF11 has anti‐aging properties, others have documented its senescence‐inducing effects. Similarly, while GDF11 has been implicated in exacerbating liver injury, it has also been shown to have the potential to reduce liver fibrosis. In this narrative review, we present a comprehensive report of recent evidence elucidating the diverse roles of GDF11 in liver development, hepatic injury, regeneration and associated diseases such as non‐alcoholic fatty liver disease (NAFLD), non‐alcoholic steatohepatitis (NASH), liver fibrosis and hepatocellular carcinoma. We also explore the therapeutic potential of GDF11 in managing various liver pathologies.


| BACKG ROU N D
The liver is a vital organ that plays an essential role in various functions within the body, including metabolism, food digestion, detoxification and vitamin storage. 1 It is subject to various chronic diseases caused by metabolic syndromes, obesity, excessive alcohol consumption, viral hepatitis and other chronic conditions.These diseases can lead to liver fibrosis, steatohepatitis, liver cirrhosis and hepatocellular carcinoma (HCC). 2,3Globally, liver diseases cause two million deaths each year and can result in severe disabilities. 4Metabolic disorders can induce fatty liver diseases.Approximately 25% of people worldwide have metabolic-associated fatty liver disease (MAFLD).
Despite the importance and burden of liver diseases, the main ways to prevent chronic liver diseases (CLDs) are preventive approaches such as reducing weight, proper vaccination against hepatitis viruses and decreasing alcohol consumption. 5Although studies have discovered new therapeutic targets for curing CLDs, enough proper therapeutics have not yet been discovered.Growth differentiation factor 11 (GDF11) protein is one of the emerging targets with beneficial effects on reducing liver fibrosis and cirrhosis. 3,6,7DF11, also known as bone morphogenetic protein 11 (BMP11), is a member of the transforming growth factorβ (TGFβ) family. 8Recent studies have demonstrated that recombinant GDF11 is an effective anti-aging agent for the heart, brain and muscles. 9ditionally, GDF11 has an impact on liver development 10,11 and liver-associated diseases like MAFLD and NAFLD, 7,12 HCC 13 and liver fibrosis. 7 previous studies, GDF11 was shown to have controversial effects on liver fibrosis and cirrhosis. 14While some studies indicated that GDF11 could impair liver regeneration 15 and exacerbate liver injury, 16 others found that GDF11 could inhibit liver fibrosis 7,17 and might protect against HCC. 13These controversies could be due to misunderstandings caused by the complexity of biological systems and the different roles of GDF11. 18In this study, we aim to explain the molecular effects of GDF11 and its roles in liver-associated diseases and the possibility of utilizing GDF11 as a drug target for these diseases.

| The physiological roles of GDF11 in the body
GDF11, is a part of BMP family that is a subfamily of the TGFβ superfamily that secretes important signalling components essential for human development. 19In humans, the GDF11 gene is located on chromosome 12q13.2and encodes a protein with 407 amino acids that is inactive after transcription. 9The GDF11 protein must be cleaved by the pro-protein convertase subtilisin/ kexin type 5 (PCSK5), a signal peptidase, and then activated by the BMP1/Tolloid family of metalloproteases. 9As a secretory protein, GDF11 is expressed in most human body tissues, including the liver, kidneys, heart, pancreas, intestines, skeletal muscles and nervous system. 20,21GDF11 induces the recruitment of activin receptor I (ActRI) by binding to activin receptor II (ActRII), leading to the formation of a complex that activates the downstream pathway with kinase functions. 9The GDF11-ActR complex activates various molecules, mainly consisting of suppressors of mothers against decapentaplegic (SMAD) and non-SMAD pathways.SMAD proteins can translocate to the nucleus and transduce signalling as transcription factors. 22SMAD mediators play crucial roles in the TGFβ signalling pathway, which is tissue-specific.TGFβ signalling can regulate the pluripotency of stem cells during embryonic development via BMP pathways and SMAD mediators. 23n-SMAD proteins are also various components that can be affected by GDF11 like mitogen-activated protein kinase (MAPK), phosphatidylinositol 3 kinase (PI3K)/AKT, and Rho-like GTPase.
Activation of non-SMAD pathways can contribute to many biological processes such as regulating inflammation and cell nucleus size. 9GDF11 regulates gene expression in different tissues via activating SMAD and non-SMAD pathways. 9F11 affects various biological functions including reducing inflammation, 24 lipid homeostasis, 25 angiogenesis 26 and anti-fibrotic properties. 14Moreover, GDF11 participates in the pathogenesis of various disorders such as diabetes mellitus, 27 cardiovascular diseases, 28 metabolic disorders, 29 cancer 18 and aging. 30Figure 1 illustrates some of the physiopathologic roles of GDF11 in the body.
GDF11 can be regarded as an anti-aging factor with anti-fibrotic properties. 14,30In different organs including the skin, neurological system, and heart, GDF11 exhibits anti-aging and regenerative properties.Its anti-aging effects may arise from features such as neurogenic and angiogenic features. 31Additionally, GDF11 can induce rejuvenation processes in tissues by stimulating stem cells. 32On the other hand, GDF11 may influence the stemness capacity of some cancer cells thereby increasing their aggressiveness. 18veral studies have reported substantial roles of GDF11 in regulating lipid and glucose homeostasis. 21,27,33GDF11 maintains insulin secretion, β-cell function, and survival in mouse models of Type 2 diabetes (T2D). 27GDF11 inhibits glucose-induced β-cell apoptosis and decreases glucagon secretion by activating TGFβ/SMAD2 and PI3K-AKT-B-forkhead box protein O1 (PI3K-AKT-FoxO1) pathways, resulting in enhanced glucose homeostasis. 21Furthermore, GDF11 inhibits adipogenesis via phosphorylation of SMAD2/3 and activation of the wingless-related integration site (WNT)/β-catenin pathway in pre-adipocytes.It also inhibits adipogenesis by increasing adiponectin expression and glucose uptake in mature adipocytes by affecting the activin receptor-like kinase 5 (ALK5)-SMAD2/3 signalling pathway. 34Consequently, GDF11 improves glucose and insulin homeostasis and reduces weight gain and white adipocyte (WAT) size. 34Walker et al. reported that administration of GDF11 reduces weight gain and improves glucose tolerance in aged mice on a high-fat diet (HFD). 33However, the precise mechanism for this enhancement in glucose uptake has not been determined but it was not due to an increase in β-cell proliferation or insulin secretion. 33erefore, further investigations are needed to discover the exact roles of GDF11 in glucose and lipid metabolism.
GDF11 is also capable of serving as a therapeutic agent.
Recombinant GDF11 has been used to rejuvenate different organs including the heart, brain, and skeletal muscles.In this process, different results were observed and different explanations were offered to explain them.Various reasons were proposed including the diversity of folding and refolding of GDF11, the variety of sources and quality of recombinant GDF11, and the concentrations of GDF11 used. 35

| GDF11 in liver development
GDF11 plays an extensive role in embryonic development.7][38][39] GDF11 has inhibitory effects on zebrafish liver development since its overexpression resulted in a smaller liver phenotype, probably due to inhibition of hepatocyte proliferation. 9,11GDF11 is a target of histone deacetylase 3 (HDAC3), an essential factor for GDF11 promoter inactivation.HDAC3 inhibition leads to GDF11 upregulation. 40HDAC3 knockout mice showed defects in liver regeneration and hepatocyte proliferation arrest in the G1 phase of the cell cycle. 41Although to the best of our knowledge, GDF11's role in liver formation has not been studied in mammals, previous studies on other species (zebrafish) and different cell lines suggested that GDF11 exerted its effects on liver development through direct action on hepatocyte precursor (hepatoblast) proliferation. 11,13,18,40Therefore, further investigations are necessary to determine the precise roles of GDF11 in inhibiting liver development and hepatocyte proliferation.
A recent study revealed that serum and hepatic expression of GDF11 increased in mouse models of partial hepatectomy.Moreover, treatment with recombinant GDF11 and adeno-associated viruses-GDF11 led to severe impairment of liver regeneration while suppressing GDF11 activity-ameliorated liver regeneration. 15cordingly, GDF11 induced cell cycle arrest and suppressed liver cell proliferation via activating the TGFβ-SMAD2/3 signalling pathway resulting in impairment of liver regeneration. 15

| GDF11 in liver senescence
GDF11 also contributes to the senescence process. 10Senescence is a biological process that shows the permanent arrest of the cell cycle and is associated with regeneration disruption, inflammation, and tumorigenesis. 42Aging is accompanied by decreased cellular autophagy which leads to the accumulation of damaged intracellular components and thereby disruption of homeostasis. 43Autophagy is an intracellular homeostatic process that results in lysosomedependent degradation of intracellular components. 44cording to Sun et al., GDF11 may downregulate liver cell autophagy by inducing the mammalian target of rapamycin complex 1 (mTORC1). 10mTORC1 is an intracellular component that suppresses autophagy via inhibiting transcription factor EB (TFEB). 45erexpression of GDF11 in aged mice resulted in increased expression of p16, one of the indicators of cellular senescence in hepatic cells. 10GDF11 indirectly decreased autophagosome-lysosome fusion, lysosome production and lysosome proteolytic activity resulting in increased cellular senescence. 10Also, knockdown of GDF11 decreased cellular senescence and increased liver proliferation due to increased autophagic flux. 10

F I G U R E 1
The contribution of GDF11 in different aspects of the pathophysiology of the human body.

| GDF11 in liver ischaemia-reperfusion injury
Ischaemia-reperfusion injury (IRI) is a complicated process that occurs during liver transplantation, trauma, shock and hepatic surgery. 46,47IRI occurs when damage caused by hypoxia and ischaemia worsens after blood flow restoration and oxygen delivery. 48,49[52][53] Serum and hepatic levels of GDF11 elevated in liver IRI in both young and aged mice.Also, administration of recombinant GDF11 resulted in aggravation of liver histologic status and liver regeneration defect. 16Cyclin D1, cyclin E1, cyclin-dependent kinase 4 (CDK4) and CDK2 accelerate cell cycle progression from G1 to the S-phase.
GDF11 could downregulate these factors by increasing p16 (inhibitor of CDK4/6) and p27Kip1 (inhibitor of CDK2) thus suppressing hepatocyte regeneration. 16Zhang et al. discovered that GDF11 improved recovery of tubular regeneration and renal function after kidney IRI in elderly mice. 54Also, another study performed by Du et al. showed that targeted delivery of the GDF11 gene to the myocardium rejuvenated the aged mouse heart and improved myocardial regeneration after IRI. 55These studies demonstrated protective effects of GDF11 in the kidney and heart after IRI in contrast to its roles in liver IRI suggesting that GDF11 expression and function may be tissue-specific. 16,54,55

| GDF11 in NAFLD and MAFLD
NAFLD is one of the world's major causes of liver disease and affects about one-quarter of the world's population. 56NAFLD is characterized by fat accumulation in more than 5% of liver weight, while other liver diseases, for example, drug-induced liver injury, excessive alcohol intake and viral hepatitis, are excluded. 56,57NAFLD is found to be associated with cardiovascular and metabolic disorders, such as obesity, hypertension, insulin resistance (IR), T2D and dyslipidemia. 58Due to the association of NAFLD with metabolic diseases, NAFLD can be counted as the hepatic indicator of metabolic syndrome. 58Regarding the strong link between NAFLD and metabolic syndrome, experts have established a new term, MAFLD, defined by the presence of hepatic steatosis with confirmed T2D, obesity, or metabolic dysregulation. 58To attribute metabolic dysregulation to someone, at least two metabolic abnormalities are required, including increased waist circumference, prediabetes, abnormal plasma triglycerides (TG), high-density lipoprotein cholesterol (HDL), blood pressure, high-sensitivity C-reactive protein (hs-CRP), and homeostasis model assessment of insulin resistance (HOMA-IR). 58ring NAFLD, hepatic steatosis occurs due to an imbalance in lipid input and export. 59Increased dietary intake, decreased mitochondrial fatty acid oxidation and decreased hepatic lipid export can result in hepatic steatosis. 59Some genetic variants, for example missense variants in transmembrane 6 superfamily member 2 (TM6SF2) and in patatin phospholipase-like domain containing protein 3 (PNPLA3) are associated with lipid imbalance resulting in inducing hepatic steatosis. 60,61Moreover, inflammation occurs during hepatic steatosis, which can lead to NAFLD progression. 62NAFLD might also progress to non-alcoholic steatohepatitis (NASH), characterized by evidence of hepatocyte injury with histological findings of steatohepatitis. 56Individuals suffering from NASH are at an increased risk of cardiovascular diseases and HCC.Chronicity of hepatocytes injury during NASH might eventually cause fibrosis and cirrhosis. 63wadays, NASH is among the leading causes of liver cirrhosis and is the second cause of liver transplantation in the United States. 56,64cause MAFLD and NASH are highly burdensome, much effort has been focused on understanding their pathophysiological mechanisms. 65In this regard, GDF11 is one of the many molecules that can interfere with pathways involved in the pathogenesis of NAFLD. 12,65i et al. discovered a higher expression of GDF11 in patients with NAFLD than in the normal population. 7On the other hand, GDF11 expression was not altered in mice fed a HFD. 7Hence, Dai et al. hypothesized that GDF11 would only increase in response to fibrosis, and in the case of HFD mice, there was neither an increase in fibrosis nor an increase in GDF11. 7GDF11 treatment of the genetically modified (ob/ob) mice neither resulted in overt hepatic lipid accumulation nor increased liver inflammation and injury.GDF11 administration in ob/ob mice could only increase activated hepatocyte stellate cells (HSCs) via influencing ALK5/SMAD2/3/AKT-dependent signalling pathways and might lead to mild profibrogenic effects in vivo; yet, GDF11 administration didn't result in an increased liver inflammation or injury.A decrease in Kupffer cell number (with an inflammatory role) was also achieved after GDF11 treatment of ob/ob mice. 12In summary, these data indicated that GDF11 may trigger the first stages of NASH development and fibrosis by HSCs activation and deposition of extracellular matrix (ECM) components in the absence of liver injury and inflammation. 12Additionally, Frohlich et al. demonstrated a considerably positive correlation between GDF11 mRNA levels and expression of genes that participated in NAFLD progression like peroxisome proliferator-activated receptor gamma (PPARγ) and carnitine palmitoyl transferase 1 (CPT1). 12 the contrary, Xu et al. found that decreased levels of GDF11 have been associated with NAFLD, increased body mass index (BMI), increased diastolic blood pressure, TG, low-density lipoprotein (LDL), HOMA-IR, fasting blood sugar (FBS), and two-hour postprandial glucose (2hpp), as well as metabolic syndrome-related morbidity in Chinese population. 29GDF11 exhibited a stronger inverse relationship with the metabolic profile in men. 29GDF11 administration in HFD mice significantly reduced NAFLD activity score (NAS), FBS, insulin level, lipid content and the expression of some genes involved in gluconeogenesis. 7A mild but significant decrease in body weight was also observed using GDF11 in HFD mice. 7Together, these data indicate that overexpression of GDF11 prevents the development of NASH in HFD mice. 7Another study on HFD mice showed that GDF11 administration increased glucose tolerance, reduced food intake, and prevented weight gain in HFD mice, but GDF11 could not inhibit age-or HFD-induced hepatosteatosis despite the improvement observed in other metabolic parameters. 33Although GDF11 involves in pancreatic development and β-cells survival, an improvement in glucose tolerance following GDF11 treatment wasn't associated with pancreatic β-cell replication or increased insulin secretion. 27,33,66,67 addition to improved glucose tolerance, insulin resistance, gluconeogenesis reduction, and weight gain inhibition, GDF11 administration decreased the number and size of lipid droplets in the hepatocytes of HFD mice and resulted in hepatic steatosis reduction. 21In HFD mice, GDF11 administration contributed to the recruitment of lipids in brown adipose tissue (BAT). 21GDF11 also increased proteins in charge of energy expenditure and thermogenesis in BAT of the HFD mice, resulting in a 0.4°C increase in rectal temperature. 21Furthermore, GDF11 prevented inflammation and macrophage infiltration in the epididymal white adipose tissue (WAT) of the HFD mice. 21In HFD mice, expression of the genes involved in fatty acid β-oxidation was not altered after GDF11 treatment. 21One possibility was that GDF11 reduced hepatocyte fat intake by altering lipid distribution and entering the lipids into the thermogenesis pathway. 21Another possibility was that GDF11 reduced metabolic disorders by decreasing inflammation, which is responsible for many metabolic complications such as obesity. 21Therefore, GDF11 increased thermogenesis, energy expenditure, and regulated glucose and lipid metabolism through TGFβ/SMAD2, PI3K/AKT/FoxO1 and AMPK pathways, which might eventually lead to the prevention of obesity and other metabolic disorders. 21e summary of the effects of GDF11 on the NAFLD models can be seen in Table 1.Regarding the impact of the GDF11 molecule in various metabolic pathways GDF11 is a promising target for the prevention and treatment of MAFLD and other metabolic disorders in the future.However, there are several inconsistencies among the results of previous investigations; Hence, more research is required to determine the different aspects of its therapeutic and potentially harmful effects.

| GDF11 in liver fibrosis
Liver fibrosis, with a prevalence of 0.7%-25.7%, is one of the leading causes of global morbidity and mortality.2][73] Therefore, understanding the pathogenesis of liver fibrosis and finding possible diagnostic and therapeutic markers is essential. 73Excessive alcohol consumption, viral infections, and MAFLD are among the leading causes of hepatic fibrosis. 14ver fibrosis is thought to be caused by the interaction of various cells including hepatocytes, HSCs, and Kupffer cells as well as the infiltration of immune cells. 74As a result of persistent and chronic liver injury, profibrotic and inflammatory cytokines increase which cause the activation of HSCs.Activated HSCs can transform TA B L E 1 GDF11 effects on the NAFLD models.into myofibroblasts which enhance the production and deposition of extracellular matrix components resulting in fibrosis. 14,75Chronic hepatic injury, inflammatory cytokine release, recruitment of inflammatory cells, and excessive ECM production (mainly collagen type I) are critical mechanisms in liver fibrosis. 73Additionally, chronic liver injury is associated with the proliferation of leucine-rich repeatcontaining G-protein-coupled receptor 5+ (LGR5+) liver progenitor cells (LPCs) which are absent in normal livers.These LGR5+ LPCs can attenuate liver fibrosis. 7,76ministration of GDF11, which is elevated in human and mice fibrotic livers, enhanced the expansion of LGR5+ cells in mouse and human liver organoids. 7In mouse models of hepatic fibrosis, LGR5+ LPCs treated with GDF11 suppressed fibrogenesis. 7,76erexpression of GDF11 in hepatic myofibroblasts may act as a growth factor to preserve LGR5+ progenitor proliferation. 7llowing transplantation of LGR5+ cells into the mice spleen, expanded LGR5+ cells reversed activated HSCs to quiescent HSC phenotype cells by downregulating actin alpha 2 (ACTA2) (a fibrogenic gene and marker of activated HSCs). 7This process may explain the underlying mechanism through which GDF11-induced LGR5+ cells decrease liver fibrosis. 77][78] Contrary to these results, Frohlich et al. showed that in obese (ob/ob) or lean wild-type mice GDF11 enhanced profibrogenic program in HSCs worsened collagen deposition and increased α smooth muscle actin (αSMA) staining in the liver without affecting hepatic damage or inflammation. 12The observed controversy regarding outcomes might result from different models employed in-vitro and in-vivo investigation procedures and route and dosage of GDF11 administration. 14nsequently, further investigations are required to determine the exact mechanism and potential therapeutic effects of GDF11 in liver fibrosis.

| GDF11 and liver cancer
HCC is the most common primary liver cancer and the third most common cancer in terms of mortality. 79,80Despite the advances in recognition of HCC and its aetiologies, 5-year survival rate of this cancer is only 21%. 81Hepatitis C virus (HCV) infection, hepatitis B virus (HBV) infection, alcoholic cirrhosis, aflatoxin-contaminated food consumption, NASH, metabolic disorders and MAFLD are among the significant risk factors of HCC. 82,83The risk factors of HCC usually contribute to liver injury by inducing chronic liver inflammation.
The chronicity of liver injuries results in liver cirrhosis which contains focal areas of immature and abnormal hepatocytes; consequently, these dysplastic precancerous areas might develop HCC. 82In some cases, HCC can be generated in a non-cirrhotic liver.Non-cirrhotic HCC is more prevalent among HCC patients with NAFLD bases. 46e to the late diagnosis of NAFLD-induced HCC, prognostic outcomes are usually worse. 84Therefore, understanding the molecular mechanisms contributing to HCC development can help manage HCC better.GDF11 is suggested to be a regulator of differentiation in cells that retain stemness capacity, like HCC cells, so these cells are potential targets for GDF11. 13,18Previously, the downregulation of GDF11 expression was discovered in patients with HCC. 85The altered expression of GDF11 in HCC models suggested that GDF11 might contribute to HCC development. 86Also, genetic mutations in TGFβ core genes, including GDF11, play an important role in HCC pathogenesis. 87,88Previous studies discovered tumour suppressive roles of GDF11 in HCC by reducing HCC cell proliferation, clonogenic capacity, cellular function, and aggressiveness, as well as causing dysregulation of cancer cell metabolism. 13,18,85,89rardo-Ramírez et al. found that GDF11 inhibits tumour progression via suppression of cellular proliferation and doesn't affect HCC cell viability. 13Additionally, cell proliferation of tumour cells was also inhibited by GDF11 in other studies. 89,90Another study mentioned a reduction in HCC cells' viability in addition to proliferation inhibition after GDF11 treatment. 85GDF11 increased HCC cells' sensitivity to cisplatin. 91Tumour aggressiveness, stemness markers, and mesenchymal markers of HCC cells also decreased after GDF11 treatment in Gerardo-Ramírez's study. 13Also, epithelial markers and cell-to-cell connections increased after GDF11 treatment of the HCC cells. 13As a result, GDF11 made a cytostatic condition and caused a decrement in epithelial to mesenchymal transition, resulting in decreased tumour aggressiveness and invasion. 13ohlich et al. declared that treatment of HCC cells with GDF11 resulted in increased expression of genes that participated in fatty acid β-oxidation lipid droplet formation and growth regulating fatty acid storage and steatosis. 90More lipid droplets with larger sizes were found in HCC cells.So an increase in lipid synthesis and a decrease in cell apoptosis were observed during GDF11 treatment.
Whereas GDF11 reduced HCC cell apoptosis and served them with lipid energy GDF11 reduced tumour progression by inhibiting cell proliferation. 90 the contrary, in Sharik Hernandez et al.'s study, GDF11 administration in HCC cells impaired both glycolysis and oxidative phosphorylation. 89GDF11 suppressed the expression of genes involved in lipogenesis and the AKT/mammalian target of the rapamycin (mTOR) pathway which participates in lipid homeostasis in HCC cells. 89Both neutral lipids and cholesterol content of the HCC cells were diminished and changes in their mitochondria such as disarrangement of cristae partial cristolysis electron-lucent matrix and reduced mitochondria size were observed.Results from this study indicated that GDF11 caused impairment of cancer cell lipid and glucose metabolism and induced defects in mitochondrial functions.
Therefore, the tumour suppressive property of GDF11 was concomitant to the decrease in cholesterol transport activity and cholesterol homeostasis. 89mour-associated macrophages are macrophages that reside in the tumour microenvironment. 92These macrophages predominantly shift to the M2 type in the HCC microenvironment and due to their immune-suppressive phenotype are related to poorer prognosis of cancers. 93GDF11 treatment of the THP-1-macrophage cell line in the HCC model resulted in an increase in polarization of macrophages to M1 macrophages.It was concluded that GDF11 treatment of HCC might inhibit tumour progression by inducing polarization of macrophages to M1. 94 An additional type of primary liver cancer cholangiocarcinoma arises from the epithelium of intra-or extrahepatic bile ducts. 95,96e incidence of cholangiocarcinoma is less than 6 cases per 100,000 people.Cholangiocarcinoma is a rare but highly fatal cancer and its incidence rate has increased worldwide during the past decade. 96Cholangiocarcinoma is mostly asymptomatic at early stages and thus is diagnosed at advanced stages leading to poor prognosis and a 5-year survival of 7%-20%. 97,98Hence, finding new biomarkers for diagnostic and therapeutic means is of great importance.
A recent study has shown upregulation of PCSK5 and GDF11 in cholangiocarcinoma patients. 13Exosomes of patients with cholangiocarcinoma exhibited elevated miR-3124-5p levels which contribute to cancer cell proliferation migration and angiogenesis through downregulation of GDF11 expression.Consequently, downregulation of GDF11 may be responsible for enhancing cholangiocarcinoma aggression. 99ble 2 summarizes the effects of GDF11 on cancers of the liver.
Based on the results of the above investigations targeting GDF11 might represent a therapeutic option in the future for liver cancers.
Therefore, more investigation is needed to elucidate the exact function of GDF11 in HCC.

| THE ROLE OF G DF11 ANALOG UE S AND LIVER-A SSO CIATED D IS E A S E S
1][102][103] Moreover, the potential therapeutic effects of GDF11 on metabolic disorders such as obesity, T2D, glucose and insulin homeostasis dysregulation, and energy imbalance were recently evaluated. 21,27,33Additionally, GDF11 analogues play pivotal roles in liver-associated diseases like NAFLD, HCC and liver fibrosis. 7,12,13However, there are inconsistencies in the impacts of GDF11 analogues on liver diseases which might be due to diversity in GDF11 dosage or the methods used for increasing GDF11 (such as recombinant GDF11 or GDF11 overexpression by plasmid or viral vectors). 33,35Also, different protein refolding efficiencies, protein sources, and concentrations might result in different recombinant GDF11 concentrations and consequent disparities in study outcomes. 35,104e promising effects of GDF11 analogues on metabolic disorders (such as obesity and T2D) and liver diseases like NAFLD, liver fibrosis, and HCC are still in early preclinical stages.Further studies are required to evaluate their efficacy and possible adverse effects. 35However, the use of GDF11 in clinics is questionable due to its low production efficiency, conflicting results about GDF11's rejuvenating effects, and the risk of inducing fibrosis. 18,35,104

99 TA B L E 3
The usage of GDF11 analogues in liver diseases.

Table 3
summarizes the latest findings regarding the effects of GDF11 analogues on liver and metabolic disorders.TA B L E 2 Effects of GDF11 on liver cancer cells.